# Cosmological histories in bimetric gravity: a graphical approach

## Abstract

The bimetric generalization of general relativity has been proven to be able to give an accelerated background expansion consistent with observations. Apart from the energy densities coupling to one or both of the metrics, the expansion will depend on the cosmological constant contribution to each of them, as well as the three parameters describing the interaction between the two metrics. Even for fixed values of these parameters can several possible solutions, so called branches, exist. Different branches can give similar background expansion histories for the observable metric, but may have different properties regarding, for example, the existence of ghosts and the rate of structure growth. In this paper, we outline a method to find viable solution branches for arbitrary parameter values. We show how possible expansion histories in bimetric gravity can be inferred qualitatively, by picturing the ratio of the scale factors of the two metrics as the spatial coordinate of a particle rolling along a frictionless track. A particularly interesting example discussed is a specific set of parameter values, where a cosmological dark matter background is mimicked without introducing ghost modes into the theory.

- Authors:

- Oskar Klein Centre, Stockholm University, Albanova University Center 106 91 Stockholm (Sweden)

- Publication Date:

- OSTI Identifier:
- 22680008

- Resource Type:
- Journal Article

- Resource Relation:
- Journal Name: Journal of Cosmology and Astroparticle Physics; Journal Volume: 2017; Journal Issue: 02; Other Information: Country of input: International Atomic Energy Agency (IAEA)

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COSMOLOGICAL CONSTANT; COUPLING; ENERGY DENSITY; EXPANSION; GENERAL RELATIVITY THEORY; GRAVITATION; INTERACTIONS; MATHEMATICAL SOLUTIONS; METRICS; NONLUMINOUS MATTER; PARTICLE TRACKS; PARTICLES

### Citation Formats

```
Mörtsell, E., E-mail: edvard@fysik.su.se.
```*Cosmological histories in bimetric gravity: a graphical approach*. United States: N. p., 2017.
Web. doi:10.1088/1475-7516/2017/02/051.

```
Mörtsell, E., E-mail: edvard@fysik.su.se.
```*Cosmological histories in bimetric gravity: a graphical approach*. United States. doi:10.1088/1475-7516/2017/02/051.

```
Mörtsell, E., E-mail: edvard@fysik.su.se. Wed .
"Cosmological histories in bimetric gravity: a graphical approach". United States.
doi:10.1088/1475-7516/2017/02/051.
```

```
@article{osti_22680008,
```

title = {Cosmological histories in bimetric gravity: a graphical approach},

author = {Mörtsell, E., E-mail: edvard@fysik.su.se},

abstractNote = {The bimetric generalization of general relativity has been proven to be able to give an accelerated background expansion consistent with observations. Apart from the energy densities coupling to one or both of the metrics, the expansion will depend on the cosmological constant contribution to each of them, as well as the three parameters describing the interaction between the two metrics. Even for fixed values of these parameters can several possible solutions, so called branches, exist. Different branches can give similar background expansion histories for the observable metric, but may have different properties regarding, for example, the existence of ghosts and the rate of structure growth. In this paper, we outline a method to find viable solution branches for arbitrary parameter values. We show how possible expansion histories in bimetric gravity can be inferred qualitatively, by picturing the ratio of the scale factors of the two metrics as the spatial coordinate of a particle rolling along a frictionless track. A particularly interesting example discussed is a specific set of parameter values, where a cosmological dark matter background is mimicked without introducing ghost modes into the theory.},

doi = {10.1088/1475-7516/2017/02/051},

journal = {Journal of Cosmology and Astroparticle Physics},

number = 02,

volume = 2017,

place = {United States},

year = {Wed Feb 01 00:00:00 EST 2017},

month = {Wed Feb 01 00:00:00 EST 2017}

}